ANTIOCH — A man who was killed after running onto Highway 4 and being hit by an ambulance Sunday night is believed to have committed suicide, authorities said Monday.

The man, a 62-year-old Brentwood resident, reportedly pulled his own car over to the shoulder and ran out into the roadway on eastbound Highway 4 at the Oakley Curve in Antioch at about 11:30 p.m. Sunday, according to the California Highway Patrol.

He was apparently struck by an ambulance, and officers responding to the scene found the man lying in the roadway. He was declared dead a short time later.